1. Field of the Invention
The present invention relates to a CLV (Constant Linear Velocity) disc applied to optical disc medium, a format of the above-mentioned CLV optical disc, and an optical disc medium recording and reproducing apparatus, in particular, the CLV disc and the CLV disc format in the large capacitance optical disc apparatus capable of recording and reproducing the information on the optical disc medium.
2. Discussion of the Background
In order to raise the speed of accessing the information recorded on the optical disc media, it is necessary to control the speed of moving the optical head precisely and with high speed. When the optical disc apparatus receives the indication of accessing the information from the upper-ranked apparatus, the optical disc apparatus calculates the relationship between the logical number of the information and the physical position as shown by the track number or the sector number on the optical disc, and the apparatus sends the optical head to the above-mentioned physical position.
Hereupon, as to such optical disc, there exist two types of recording method; those are, a CAV (Constant Angular Velocity) type recording method in which the angular velocity is constant and a CLV (Constant Linear Velocity) type recording method in which the linear velocity is constant.
In the CAV type method, since the amount of the information on one track is always constant regardless of the inner and outer circumferences of the disc, the logical information number and the track number (numerical value) can be easily calculatively converted from each other, and thereby the calculation thereof can be done in a very short time. However, according to such CAV type method, there arises a problem that the line density of the information at the outer circumference of the disc is lowered and thereby the entire memorizing capacity is lowered. In order to avoid such unfavorable problem, in a method called “modified CAV type method”, it is devised that the frequency of the recording signal is raised at the outer circumferential portion of the disc for the purpose of making uniform the line density on the respective inner and outer circumferential portions. However, in such way as mentioned above, there arises another problem that the structure of the formatter electric circuit becomes complicated.
From the viewpoint of the memorizing capacity and the simplification of the formatter electric circuit, the CLV type method is more preferable than the CAV type method. However, in the CLV type method, the amount of the information on one track differs in accordance with the radius position on the disc, and the calculative conversion between the information number and the physical position may become further complicated. As a result, the calculation of conversion therebetween cannot be done in a short time, and thereby, the access time may be elongated. Those matters are the problems of the CLV type method to be solved.
In recent years, as large-capacity optical disc media, DVD-ROM, DVD-R, and DVD-RAM, etc. have become popular, the requirement of increasing the memory capacity of these media continues to grow. Namely, it is desirable that the pitch be narrowed more and more and that the bit is made smaller. In such a situation, providing high-speed access to such an increased large-capacity media has become an important problem to be solved.
In order to solve the above mentioned problem, the published specification of Japanese Laid-Open Patent Publication No. 9-16980 filed by Nihon-Denki Co., Ltd. entitled, “A METHOD OF ACCESSING THE INFORMATION OF THE CLV OPTICAL DISC” has already described the method composed of the steps of: firstly determining only the moving direction of the optical head; driving, in advance, the optical head moving medium; obtaining, thereafter, the present position (track number) corresponding to the present address and the target position (track number) corresponding to the access target address by the calculation; calculating the track number therebetween (between the present position and the target position); and finally performing the access control.
However, there is a limitation in the realization of the high-speed operation obtained in such way as mentioned heretofore. Therefore, sufficient high-speed access cannot always be realized.
On the other hand, the published specification of Japanese Laid-upon Patent Publication No. 8-279129 filed by SONY Co., Ltd. entitled, “A METHOD OF MANUFACTURING THE CLV DISC” does not describe technology relating to the method of providing the usual CLV format. Instead, it describes the technology relating to a method of arranging sectors without causing any angular positional error obtained at the time of ideally driving with CLV. The above specification has already described the method composed of the steps of: causing the formatter to receive the start position of the start sector's address from the cutting machine with the same angular information; previously estimating the address situated at the same neighboring angular position as that of the start address by the calculation; changing the buffer length when the sector arrives at the above-mentioned estimated address; confirming thereby the arrival of the electric signal of the angular information sent from the cutting machine; sending the address signal of the next sector and thereby absorbing the variation of the angular position due to the error of the cutting start radius position and due to the change of the track pitch; and making uniform the sector angle between the different stampers.
However, according to the method as mentioned above, it is inevitably necessary to provide special processing such as the estimation of the sector arriving at the same neighboring angular position as that of the start sector and the compensation of the buffer length, etc.
As mentioned above, the background-art CLV optical disc requires a lot of time for performing the calculative conversion between the logical information number and the physical position. Therefore, the speed of accessing the disc information is inevitably lowered. This is a problem to be solved.
To provide a large capacity optical disc medium, it may be profitable to adopt the CLV (Constant Linear Velocity; Line Speed-Constant) format in which the line density of the information becomes constant. However, in the CLV format, in the case of accessing a specified sector, it is required to perform the control operation such that the revolution rate of the spindle motor for rotating the disc is changed in accordance with the disc radius position on which the sector exists and the scanning line speed of the reproducing track is made constant.
On the other hand, while the CAV (Constant Angular Velocity; Angular Velocity-Constant) format is inferior in terms of storage capacity, it is superior as to case of accessing. Namely, the respective sectors are arranged on the radius line of the disc, and all of the sectors can be accessed using the same disc revolution rate at the time of reproducing.
Furthermore, there exists an MCAV format taking advantage of the large capacity of the CLV format and the high-speed accessing of the CAV format. In the MCAV format, plural zones are provided in the radius direction of the disc, one circle of the track is divided into plural pieces of the sector in each of the respective zones, and the number of the divided sectors is increased toward the outer circumferential zone of the disc, and then the distribution of the information amount in the radius direction of the disc is approximated (brought close) to the information distribution of the CLV format and the respective sectors are aligned in the radius direction per each of the respective zones. In such format, regarding the movement between the zones, although it is necessary to change the revolution rate of the disc or to change the frequency of the clock for recording/reproducing under the condition of making constant the revolution rate, the high-speed accessing of the CAV format can be obtained in the respective zones.
The method of accessing disc tracks of discs having these formats is discussed below. At first, as shown in FIG. 11A, regarding the CLV format, the revolution rate of the disc is controlled such that the line speed of scanning the track becomes equal to a predetermined value for the track on the radius position of the specified disc or for the track on the radius position where the pickup is situated now, by use of the period of a specified reproducing data signal or the wobble signal obtained from the zigzag movement of the constant period previously assembled (established) on the track at the time of making the master board.
At the step of controlling the disc revolution number, the address information is decoded and thereby the present address value can be obtained. Next, the seeking operation is started from the difference between the present address and the target address. In the CLV format, the arrangement of the respective addresses is different from each other for the respective discs generally due to the difference of the line speed settings at the time of making the master board or due to the slight (very small) line speed error, etc. in spite of intending to perform the same settings.
Consequently, the seeking operation is performed as follows: Assuming the designated place of the target address, when the pickup is moved it counts the number of the transverse tracks. At the time when the pickup arrives at the assumed track, the address value is acquired again and the difference between the acquired address value and the target address value, if any, is determined. When the former differs from the latter, the position of the target address is assumed again, and the abovementioned operation is repeated until the acquired address arrives at the target address. At this time, the disc revolution rate is always controlled corresponding to the reproducing address position.
Next, the CAV format is described. As shown in FIG. 11B, the revolution rate of the disc is set to a predetermined revolution rate. At this time, the address information of the optional track can be obtained. The address value is obtained, and then the seeking operation is performed from the difference between the obtained address and the target address. In the CAV format, since the arrangement of the respective sectors is definite, it turns out to be possible to arrive at the target address precisely and with high speed by just counting each transverse track number at the time of performing the seeking operation.
On this occasion, it is not necessary to control the revolution rate of the disc as in the case of the CLV format. However, even in this case, it is necessary to set the predetermined revolution rate and to acquire the address value when the present address value is obtained, as in the case of the CLV format.
In the MCAV format, as shown in FIG. 11C, the arrangement of the sector having the respective address is clearly defined. Therefore, the seeking operation to the target address can be precisely done with high speed as in the case of the CAV format. However, in the seeking operation of striding (stepping over) the zones, it turns out to be necessary to control the disc revolution rate of the disk or to control the frequency of the recording/ reproducing clock. Even on this occasion, regarding the acquisition of the present address value which is the first operation of seeking, it turns out to be necessary to set the revolution rate to a predetermined revolution rate.
For instance, the published specification of Japanese Laid-open Patent Publication No. 6-231469 discloses the featured address ID data modulated with BPM (Bit Position Modulation) by way of the PE (Phase Encoding) as a background art and recorded on the recording medium. The art does not require any special sector mark and realizes the preferable sector synchronization, and enables to calculate the line speed information of the track from the interval between the detection pulses of the address part. The above-mentioned operation itself is performed on the basis of the disc rotation control corresponding to the position in the radius direction of the disc and the reproduced address value. And then, since there scarcely exists the correlation between the address ID data and the data modulated and recorded with PWM (Pulse Width Modulation), the sector synchronization and the detection of the address ID can be preferably performed in synchronism with each other. In addition, the basis speed of the track can be presumed (assumed) on the lines of the pulse width given (created) by the phase encoding (PE), and thereby the high-speed accessing can be realized.
Furthermore, the specification of Japanese Patent No. 2,689,980 relates to the seeking control in the CLV disc format and discloses the method of the seeking control, in which the wobbling signal of the predetermined frequency is modulated with the address information coded by a frequency lower than the predetermined frequency and the address information is extracted from the wobbling track of the optical disc which is wobbled and thereby formed corresponding to the modulated signal, and in such way the seeking operation is controlled.
Furthermore, the published specification of Japanese Laid-open Patent publication No. 5-266497 discloses the method of the seeking control in the CLV disc format, in which the offset value for the short-distance access and the offset value for the long-distance access are previously programmed, the offset value is selectively used in accordance with the distance to the place to be accessed, and then the track jumping is performed. In such seeking method, the accessing operation can be intended to speed up.
Furthermore, according to the method of accessing the information of the CLV optical disc discloses in the published specification of Japanese Laid-open Patent publication No. 9-16980, the number of the tracks for moving is calculated from the difference between the present track number and the target track number, the track jumping or seeking operation is performed. However, in such background-art method, there arises a problem to be solved that the accessing operation may be delayed, because the calculation of the logical information number and the physical track position takes a long time, regarding the information accessing of the disc recorded by the CLV method. In the above-mentioned background art, only the moving direction of the optical head is firstly determined, the optical head conveying medium is driven in advance, the present position (track number) corresponding to the present address and the target position (track number) corresponding to the target position (track number) corresponding to the accessing target address are obtained by the calculation, and the number of the tracks therebetween is calculated and thereby the control of accessing can be performed.
With the development of the Laser technology, the optical disc medium has been widely used as the recording/ reproducing medium and satisfied the demand of large memorizing capacity as DVD-ROM, DVD-RAM, and DVD-R, etc. In order to realize a large memorizing capacity, narrow pitch and small pit are always successively required for those optical disc media.
As to the large memorizing capacity, the CLV disc format capable of realizing the constant line density of the information recording may be profitable. However, in such CLV disc format, when the intended sector is accessed, it is necessary to control the scanning line speed of the reproducing track so as to make it constant by changing the revolution rate of the rotating motor corresponding to the radius direction of the optical disc medium in which the sector exists. As the result, the control of the optical disc medium may become further complicated.
On the other hand, the CAV disc format is profitable in that the respective sectors are arranged on the radius line of the optical disc medium, the accessing with the same revolution rate can be done for every sector at the time of reproducing, the revolution rate of the optical disc medium is set to the predetermined revolution rate, the address value of the optional track is taken in, the seeking operation is done on the basis of the difference between the address value thus taken in and the target address value, the number of tracks traversed is counted, and in such way the operation of accessing the target address can be done effectively.
However, in the above-mentioned CAV disc format, the memorizing capacity per one track is determined by the number of the recordable marks in the recording area of the optical disc medium, and therefore the problem of the large memorizing capacity has arisen.
Furthermore, an M-CAV (Modified CLV) disc format has been also used. The M-CAV takes in the large memorizing capacity of the CLV disc format and the high-speed accessing of the CAV disc format.
In such M-CAV disc format, plural zones are provided in the radius direction of the optical disc medium, the entire circumference of the track is divided into plural sectors in the respective zones, the number of the divided sectors is gradually increased toward the outside zone in the radius direction, and the recording distribution of the information amount in the radius direction of the optical disc medium is approximated to that of the CLV disc format.
Furthermore, in such M-CAV disc format, the respective sectors are arranged in the radius direction per each of the respective zones, the recording frequency is set so as to gradually increase it, and therefore the high-speed accessing of the CAV format can be obtained in the zone.
The background arts in connection with the CLV drive controlling method of the spindle motor and the slide motor and the CLV format in the optical disc cutting machine are described hereinafter.
The published specification of Japanese Laid-open Patent Publication No. 6-36272 relating to the rotation of the disc (corresponding to Japanese Published Patent Publication No. 6-36272) discloses the control operation, in which one time period of the rotation pulse obtained from the rotation pulse generator mounted on the spindle is counted with the constant value by the pulse train obtained from the radius signal generating unit for obtaining the radius signal having the value corresponding to the radius position where the optical pickup exists and the variable frequency generating unit capable of modulating the frequency so as to make constant the product of the radius signal and the frequency, the error of the calculated value is fed back to the speed, and thereby the line speed of the optical disc on the optical track.
The published specification of Japanese Laid-open Patent Publication No. 8-235769 relating to the method of controlling the motor revolution rate and the apparatus for practicing the above controlling method discloses the method of obtaining the revolutions rate variation further approximated to the revolution rate variation in the ideal CLV method by the following two methods:                (1) A motor rotation controlling method of controlling the motor rotation by stepwisely reducing the variation rate of changing the number of revolutions of the motor corresponding to the positional variation of the optical disc in the radius direction; and        (2) A motor rotation controlling method of successively and alternately providing the first section (block) in which the motor rotation is controlled by stepwisely reducing the variation rate of changing the number of revolutions of the motor corresponding to the positional variation of the optical disc in the radius direction and the second section (block) in which the motor is rotated with a constant number of revolutions and controlling the rotation of the motor in such first and second sections as mentioned above.        
The specification of Japanese Patent No. 2,844,565 relating to the CLV controlling apparatus discloses the method of controlling the revolution rate of the spindle on the basis of the target line speed data and the radius position data.
The published specification of Japanese Laid-open Patent Publication No. 8-279192 describes the method of manufacturing the CLV disc. The Laid-open Patent does not directly relate to the CLV controlling method. Instead, it relates to the arrangement of the sectors without any angular position error which can be obtained in the case of performing the ideal CLV drive at the time of cutting the CLV disc format.
The formatter receives the start position of the start sector address with the same angle information from the cutting machine. The address coming close to the same angle as that of the start address is previously estimated by the calculation. When the sector comes at the above address, the buffer length is changed, and then the arrival of the electric signal of the angle information sent (transmitted) from the cutting machine is confirmed, and then the address signal of the next sector is sent out. In such way, the error of the cutting start radium position and the variation of the angular position due to the track pitch variation can be absorbed. Thereby, the sector angles between the different stumpers can be aligned (made uniform).
Regarding the method of evaluating the CLV drive accuracy of the spindle motor or the slider in the optical disc master board exposing apparatus, the method of controlling the CLV drive, and the apparatus for practicing those methods, it is noticed that the phase difference of the pulse train having the constant period length between the adjacent tracks due to the fundamental clock linearly changes.